A dense bed of light-sensitive bacteria has been developed as a unique kind of photographic film. Although it takes 4 hours to take a picture and only works in red light, it also delivers extremely high resolution.

The "living camera" uses light to switch on genes in a genetically modified bacterium that then cause an image-recording chemical to darken. The bacteria are tiny, allowing the sensor to deliver a resolution of 100 megapixels per square inch.

To make their novel biosensor, Chris Voigt’s team at the University of California in San Francisco, US, chose E. Coli, the food-poisoning gut bacterium. One of the reasons for that choice is that E. Coli does not normally use light - photosynthesising bacteria could have used light to prompt other, unwanted, biological processes.

The researchers used genetic engineering techniques to shuttle genes from photosynthesising blue-green algae into the cell membrane of the E. coli. One gene codes for a protein that reacts to red light. Once activated, that protein acts to shut down the action of a second gene. This switch-off turns an added indicator solution black, reports New Scientist.

"We're actually applying principles from engineering into designing cells," said Christopher A. Voigt, assistant professor of pharmaceutical chemistry at the University of California, San Francisco, and a leader of the photography project, which is described in a paper being published today in the journal Nature.

One team of synthetic biologists is already trying to engineer bacteria to produce a malaria drug that is now derived from a tree and is in short supply. And J. Craig Venter, who led one team that unraveled the human DNA sequence, has said he now wants to synthesize microbes to produce hydrogen for energy.

The technology could also be used to create new pathogens or synthesize known ones.

The scientists created sort of a chain reaction inside the bacteria. When the bacteria are in the dark, the enzyme is produced, turning the medium black. When the bacteria are exposed to light, production of the enzyme is shut off, informs New York Times.